This article provides an overview of the differences between additive and subtractive manufacturing, 3D printing technologies, 3D printing applications for aerospace and defense parts, and a look at how Primus utilizes titanium printing to support customers.
What is the difference between additive and subtractive manufacturing techniques?
Additive manufacturing, also known as 3D printing, is the process of creating an object, such as a critical satellite component, using material deposition and numerous post processing techniques. This is different than traditional subtractive manufacturing in one main way. Instead of taking a block of raw material and using lathes, mills, and CNC machines to remove material in a controlled manner, material is selectively added to a blank slate to build a component from the ground up. Subtractive manufacturing typically
uses cutting tools such as end mills, boring bars, or drill bits to remove matter from a block, bar, or slug of raw material. The tool (or the material if the machine in question is a lathe) is spun at a rapid rate and is ran through the material at computer programmed locations where stock needs to be removed. Through 3 and 5 axis machining, the work can be spun along various axes to remove material to form complex shapes. One alternative to subtractive manufacturing is 3D printing.
This seemingly new technology can be traced back to 1925. A patent was issued for the use of arc welding techniques to create sculptures and decorative articles by depositing welded beads of metal on top of one another to form baskets and other household items. 3D printing first found its use in manufacturing in 1982 when United Technologies Research Center filed a patent for a “Method for Fabricating Articles be Sequential Layer Deposition.” Initially, Additive Manufacturing was only used for rapid prototyping to develop a model for parts to be later created using subtractive methods. It wasn’t until the 2000’s that Additive Manufacturing began to achieved production-grade parts primarily for the medical implant industry. Since then, additive manufacturing has crossed over to the Aerospace and Defense supply chain for making high precision, low volume parts and components.
What are the key types of additive manufacturing / 3D printing?
- Stereolithography – This method utilizes liquid plastic to create 3D objects through layer-by-layer deposition. Liquid resign is collected in a vat with a clear bottom. UV light is used to trace a pattern in the vat and selectively cure the resin. The object is dragged up by a platform to allow the part to grow from the base down . This type of 3D printing is primarily used for rapid prototyping as it is too slow to produce plastic parts in a cost-effective manner.
- Fused Deposition Modeling – Fused Deposition Modeling feeds a thermoplastic filament into an extruder. This plastic is then deposited onto a plate to build a part layer-by-layer from the ground up. This is the most common type of 3D printing and is often seen in entry level printers. This method is also used for rapid prototyping and can be used along with Stereolithography to create negative molds for metal casting.
- Sheet Lamination– Sheet Lamination utilizes a cutting device (usually a laser) to slice through thin layers of material. These cuts are then deposited layer-by-layer and glued together to form parts. This strategy can be used with plastics, wood, and even metal to create prototypes and production level parts.
- Powder Bed Fusion– This strategy employs a laser or electron beam to weld or sinter layers of powdered metal together to from a part. Powder bed fusion is commonly employed by the Aerospace, Defense, and medical industries to create intricate, low volume production parts. The printer used by Primus Aerospace falls under this category.
What types of aerospace projects are best performed on a 3D printer?
- Prototype parts – Producing 3D printed parts requires very little setup, additional tooling or fixtures to create working parts for prototype or R&D applications. This allows design modifications to be verified with minimal effort. Engineers may 3D print a part for a prototype but later transition to precision machined parts as the program enters production phase.
- Complex designs – 3D printing allows designers to create parts that could not be produced with traditional subtractive manufacturing techniques. While aerospace parts designers should not throw out the book on design for manufacturability (DFC), some applications do require designs that cannot be accomplished on a 5-axis CNC mill (such as integrated internal pathways and complex internal features).
- Lightweight requirements – Additive manufacturing allows the incorporation of weight saving features and innovative designs that cannot be traditionally machined, such as complex lattice structures and intricate hollow structures. For example, aerospace engineers designing parts for a commercial satellite (where weight represents a high-payoff Value Engineering effort) can shed costly weight without sacrificing strength.
- Low production volumes – One drawback of 3D printing is its part production time. For a powder bed fusion system, builds take at least one day to print causing this technology to not be applicable for high production parts (yet).…
Additive Manufacturing at Primus Aerospace
Primus primarily uses a Velo3D Sapphire Metal AM Printer for additive manufacturing aerospace projects. This machine is tailored to use powder bed fusion technologies to 3D Print space and satellite parts using a Ti 6Al-4V titanium alloy powder..
ThisThe Velo3D Titanium Printer works by using a vacuum powered contactless recoater to deposit titanium powder over a build plate. The recoater dumps material over the plate, and then uses a vacuum to suck up any access metal an
d ensure a consistent layer of powder. Two separate lasers sinter fuse the powder together in a predetermined pattern to methodically form a part from the base up. Fusion is the process of melting a two separate solid components and re-solidifying them together. This is done in layers that are slightly offset from one another to avoid empty space in the finished product. This ensures strength and reliability in precision aerospace parts. This is done on top of a build plate that sits on top of a piston, which lowers the plate to accommodate for each subsequent layer of titanium until the build is complete. The lasers and piston take instructions from Velo’s Flow software. This takes a CAD model of a part, slices it, and creates step by step instructions for the 3D printer to follow.
This machine has the capability to print material at low angles, parts with overhanging features, as well as internal passageways and cavities with little to no support structures. In turn, this decreases the need for post processing and allows primus to manufacture an extremely wide range of components. So far, we have used this machine to create one-piece parts with a high level of complexity, components with internal cooling passages, and thin-walled pressure vessels with an almost unattainable degree of precision.
Primus Aerospace supports aerospace, defense, and space manufacturers with build to print 3D printed titanium parts. Primus is able to combine this innovative 3D printing technology with other valued added services (such as finishing, grinding, or painting) and an aerospace AS9100 certified quality management system.
By Josh Trujillo
Images courtesy of Velo3D